Set variable/Array to a length by scripting

In my script is getting complex and I get a point that I don't want to set the length or size of a variable/Array so I would like to know how I can set a variable length using a variable.

Examples: (this ways doesn't work, that's why in need the correct form to do it)

var example : float[mylength];
//or also
example.Length = myLength/*or myLength.Length*/;

so that way I don't have to put

var example : float[];

and then put the length or size by manually.

You can do this:

var example : float[];

function Start () {
    example = new float[myLength];

I'm not clear if that's what you're trying not to do, but if so, I don't know why.

var example: float[];
example[myLength] = 0;

now the example variable is length of myLength. I believe you can only set the length like this once. If you do this at one point, and then you try to set a value at a greater length (eg. example[myLength+1]) it will error.